In order for elevator cabs to properly align with landing door sills prior to opening the cab and landing doors to discharge and/or take on passengers, the vertical position or location of the cab in the elevator hoistway must be very accurately established. There are two general types of cab position information that must be provided to the elevator microprocessor controller in order to properly operate the elevator in a safe manner. These are: gross cab position when the cab is outside of a called landing zone; and fine cab position once the cab has entered a called landing zone. It will be understood that a "called landing zone" is one to which the elevator controller has, for some reason, dispatched the cab, and at which the cab and landing doors will be opened to accept or discharge passengers.
In order for an elevator system to operate at maximum efficiency, especially in high rise, and ultra high rise, high speed elevator systems, it is very important that the elevator cab move at high speeds between called landings during an optimum proportion of the landing-to-landing transit time. The requirement of high landing-to-landing transit speed also depends on effective cab acceleration and deceleration distances in order to maintain passenger comfort. Thus, the elevator controller must know at all times the position of cab between called landing zones. Present systems utilize a position transducer in the machine room to monitor drive shaft or traction sheave rotation in order to derive the gross position of the cab between called landing zones.
Once the cab enters a called landing zone, the fine cab position is sensed by monitoring a calibrated tape which is suspended in the elevator hoistway. The tape is used to determine when the cab door sill and landing door sill are properly aligned so that the doors can be opened to discharge and accept passengers. The tape is a metal tape which has its ends fixed to the top and bottom of the hoistway. There are spaced-apart detectable calibrations on the tape which indicate where in the hoistway the cab is located. These calibrations will determine cab positions within one-quarter of an inch relative to the hoistway walls. The calibrations can take the form of spaced magnetic strips on the tape. As previously noted, the tape is secured to the hoistway at its ends, and thus its medial portion is not fixed relative to any vertical plane in the hoistway. The portion of the tape between its ends is thus free to twist in response to hoistway turbulence, building sway, or the like. In addition, the cab will oscillate forwardly and backwardly to some extent as it moves up and down in the hoistway along its guide rails.
The tape is sensed by electrical sensors which are mounted on the elevator cab assembly, typically on the cab assembly frame. These sensors can be electro-magnetic or optical transducers. The sensors are operably connected to the elevator controller so as to transmit cab position signals to the controller at appropriate times. At the present time the sensors and their operating electronic components are disposed in a housing which includes guides that embrace the tape so as to ensure proper alignment of the sensors and the tape calibrations as the elevator cab moves up and down in the hoistway. The guides are fixed to the sensor housings. The sensor housings are mounted on brackets which are fixed to the cab frame.
In order to accommodate extant deflections of the tape which deviate from the relatively fixed vertical path of travel of the elevator cab, the sensor housings and associated tape guides are movably mounted on the cab frame mounting brackets. The sensor housings can thus move translationally on the mounting brackets whenever the guides encounter tape deflections that induce such translatory or oscillating movement. The present mounting system has proven to be operative, and is able to properly position the sensors and tape calibrations so as to provide accurate position signals to the controller; however, it does create a noise problem due to the oscillations of the sensor housings on the fixed cab mounting brackets. This noise problem is particularly bothersome during the high speed motion of the cab between landing zones, since the sensor guides must necessarily engage the tape even when the sensors are not functioning due to the cab being positioned outside of the landing zone. Passenger comfort would be enhanced if this tape guide-generated noise were eliminated or sharply reduced.